Area-Depth Strain Analysis More Details

What is an Area-Depth Graph?

For fault-related folds, an area-depth graph is created by plotting of the structural area of deformed horizons (e.g. the area of a fold) against the "regional" horizon depth. In structural settings where area is conserved during deformation, the variation in structural area with depth is a linear relationship. This linear function can be used to determine structural displacement, horizon strains, as well as the location and dip of controlling fault at depth.

When should I use Area-Depth Strain Analysis?

We recommend that the area-depth graph analysis is a good starting point to analyze and understand a folded or faulted section, when a pre-growth section is present and well-imaged. The analysis will immediately give you information about the structural styles and whether your section is balanced.

Is Area-Depth Strain Analysis difficult to do?

You can create an area-depth strain analysis of an (approximately) 2D folded structure in your area of interest in a matter of minutes:

Generate an image of the seimic section, together with any horizon and fault interpretation.
Create a new StructureSolver dolution with your saved image.
Calibrate the image, and draw your interpretation
Select the Create Area Depth graph menu item and add your horizons to the area-depth graph.
The area- depth graph is instantly plotted on the section, together with the estimated fault position,displacement vectors and strain estimates.

Now you can start to explore the structural implications of your interpretation!

What happens if I change my interpretation?

All components of the area-depth graph - the plot, the predicted fault location, the strain estimates and displacement vectors - update instantaneously as you modify your interpretation, or reconfigure the area-depth graph. The interactivity is great for exploring alternative interpretations, and identifying uncertainties and errors in the interpretation.

What controls are available to alter the Area-Depth Graph?

When you create an area depth graph and add horizons to it, the horizontal and depth limits of the area-depth analysis region are automatically set but can be interactively adjusted at any point in the workflow. StructureSolver uses regression analysis of the area-depth curve to identfy the pre-growth horizons that can be used to estimate fault location. Simple controls are provided so that users can interactively exclude horizons from the analysis and restrict the horizontal extent of the included horizons. Area-depth results dynamically update as soon as any of the controls of the area-depth graph (or the interpretation) are changed.

What are the limitations of Area-Depth Strain Analysis?

The minimum requirement for performing an area-depth graph analysis is that you have interpreted at least two horizons across one or more structures of interest. Furthermore, these horizons should be pre-growth horizons in order to estimate the fault location. The accuracy of the estimate will increase as more pre-growth horizons are included.

Area-Depth Strain Analysis works for complex, composite structures, provided that there is a common detachment or underlying fault. If there are multiple levels of detachment in your section, the technique may still work. However the analysis of the derived numerical data is more complex. Please refer to our private website material for further discussion.

If there is a mobile layer (e.g., salt or shale) immediately above a detachment, naive use of the area-depth graph technique will result in an incorrect estimate of detachment depth (usually too deep). We have extended the method to treat such cases.

I am a geologist/geophysicist doing interpretation of large data sets. How can Area-Depth Strain Analysis help me?

You can use the Area Depth Strain analysis in StructureSolver in conjunction with any interpretation system. You will easily be able to:

Rapidly assess balance of a structural interpretation
Validate interpreted fault locations
Identify high-strain horizons
Guide fault interpretation in situations where the shallow structure is well imaged but deep fault location is unknown.

I am a structural geology specialist. How can Area-Depth Strain Analysis help me?

StructureSolver can provde you with detailed, rigorous analysis of 2D sections. In particular, StructureSolver can help you:

Determine fault displacement history from growth strata
Use layer parallel strain profiles to characterize kinematic style of deformation
Map out variations in fault geometry such as ramp-flat-ramp transitions
Quickly compare changes in displacement and strain for multiple sections within a 3-D volume.

You can use the 2D analyses to guide construction of full 3D structural models and save days or even weeks of time.

My faults do not sole into a horizontal detachment. Can I use Area-Depth Strain Analysis?

Our structural geologists have extended the area-depth graph method of Epard and Groshong to handle dipping faults. This method is implemented in StructureSolver only. Please contact us for scientific and technical details.

I suspect that there may be multiple detachments at different depths. Can I use Area-Depth Strain Analysis?

The area-depth analysis is more complex in the presence of multiple detachment levels, and requires careful interpretation. However, you can gain a lot of insight into the development of the structures by exploring the area-depth graphs for different sections.. Please contact us for examples and more information.

I suspect that there is a mobile salt/shale layer in my structure. Can I use Area-Depth Strain Analysis?

In StructureSolver, you can vary the Intercept area to account for mobile material. In many cases, this option will enable you to get limits on the amount of material that has flowed into the structure. Please contact us for examples.

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